Arsenal have confirmed Kieran Tierney dislocated his shoulder in Monday's 3-1 win over West Ham, as a lengthy absence beckons.

Scotland international Tierney signed from Celtic in August for a reported £25million to bolster the left side of their defence, but his impact has been minimal due to injuries.

He joined the club during rehabilitation for a pelvic injury, limiting him to 11 appearances across all competitions.

The 22-year-old started each of Arsenal's two most recent matches, but he lasted only 29 minutes at West Ham after falling awkwardly in his own penalty area.

After receiving medical attention, Tierney gingerly walked off the pitch using his jersey as a makeshift sling. Arsenal announced the nature of his injury in a short bulletin on Wednesday.

A timescale for his return has not been provided, but he will not play again this year and is a doubt to feature in January.

Hector Bellerin sustained a hamstring injury during the warm-up before the West Ham win and is being monitored ahead of Sunday's visit of Manchester City, with the match against Standard Liege on Thursday coming too soon for him.

Nicolas Pepe, who scored only his second Premier League goal on Monday, will also miss Thursday's Europa League clash due to a bruised knee, though he has not been ruled out of the City match.

Granit Xhaka is out of both upcoming matches, however, after he sustained concussion at West Ham.